In the preparation of (meth)acrylic monomers, there are many vapor-liquid contacting operations in which it is necessary to uniformly distribute a liquid stream over a large cross-sectional area within a process vessel. The majority of these process operations involve the collection or purification of (meth)acrylic monomer streams, such as for example quenching, condensing, absorbing, and distilling operations. These operations are typically performed in process vessels resembling upright cylinders, such as towers and columns. Such process vessels commonly range in diameter from about 0.3 meter (1 foot) up to about 9.2 meters (30 feet).
Liquid distribution equipment is generally located in the upper part of the process vessel above any contact-enhancing internal components that may be present. In operation, process liquid passes through the distribution equipment, is divided and broken into a series of sheets, streams, and droplets, and then flows downward through the vessel under the influence of gravity, while vapors simultaneously pass upward through the vessel. Mass and energy transfer between the liquid and vapor occurs across the surface of the liquid; process efficiency is enhanced when there is a high liquid surface area to promote contact with the vapor, such as when a large number of liquid droplets are uniformly distributed throughout the cross-section of the vessel.
Various types of liquid distribution devices include pipes, trays, troughs, rotating armatures, and spinning disks. Such devices are intended to distribute liquid flows over a large area and frequently are combined with other internal components, such as packed beds, structured packing, or distillation trays, which serve to further distribute liquid flow in an effort to maximize coverage and generate large amounts of liquid surface area. These devices include stationary distributors, such as those described in U.S. Pat. No. 3,969,447, which describes a typical piping-based distributor comprising bottom-mounted spray nozzles, and U.S. Pat. No. 3,392,967, which describes a typical trough-type distributor. Distributors are also described that revolve about a central axis by means of being mounted to a rotating shaft (U.S. Pat. Nos. 3,079,092; 1,464,816; U.S. Pat. No. 470,375; GB 1161560). Examples of such distributors are also described in GB 726151, which describes a rotating trough comprising bottom drain tubes, and U.S. Pat. No. 3,353,802, which describes a combination of a rotating distribution armature and baffles for use in vessels of rectangular cross-section. Finally, spinning disks of various configurations have also been proposed as means for distributing concentrated liquid feed streams; such devices are for example described in US Patent application No. 2011/144384, in which a Continuous Stirred Tank Reactor (CSTR) feed stream is vigorously deflected by a spinning disk mounted on the agitator shaft.
Current liquid distribution devices, however, have a disadvantage in that they provide large process-facing surfaces within the vapor spaces of (meth) acrylic monomer process vessels on which monomer vapors may condense and form polymer accumulations. The accumulation of polymeric solids is a common problem for the preparation of (meth)acrylic monomers because the foulants may interfere with the proper operation of the vessel and disturb the intended chemical processes occurring within the vessel. Eliminating the foulants may require costly cleaning operations and process downtime. In particular, the formation of condensation polymer in the vapor spaces of (meth)acrylic monomer process vessels, such as quench vessels, absorbers, contact condensers, scrubbers, heat exchangers, distillation columns, reactors, and storage tanks, is a well-known and ongoing problem. A quench vessel may also be known as a quench column, spray cooler, quench cooler, contact cooler, and quench system.
Condensation polymer forms within process vessels when (meth)acrylic monomer vapors condense on process-facing surfaces in the absence of polymerization inhibitors. Process-facing surfaces on which condensation polymer accumulations are known to occur include the top head and walls of process vessels; the interior surfaces of vessel nozzles and manways; instrumentation and emergency pressure relief devices; internal structures such as distillation trays, packing, baffles, and support structures; and even on the interior surfaces of process piping directly connected to such vessels. For example, U.S. Pat. No. 3,717,553 teaches that dry wall regions under distillation trays are prone to polymer accumulation and recommends wetting them; U.S. Pat. No. 7,892,403 teaches that the supports for stationary spray nozzles can accumulate condensation polymer & recommends placing such support members outside of the vessel; and U.S. Pat. No. 6,983,758 teaches that the presence of stationary spray nozzles and associated supply lines provides surfaces for the accumulation of condensation polymer and that low flow regions such as nozzles and manways are also prone to condensation polymer accumulations.
There are many variations of tank cleaning nozzles used to clean process vessels. A common feature of tank cleaning nozzles is the reliance on highly pressurized sprays or liquid jets to dislodge accumulated foulants through liquid impact. These devices are intended to be used intermittently, during cleaning periods when process equipment is not operating. Furthermore, any fouling-material dislodged must still be removed from the process vessel, or it will merely transfer the fouling problem to a different part of the process.
Thus, there is a need for liquid distribution equipment and/or methods which can uniformly distribute liquid over the internal cross-section of (meth)acrylic monomer process vessels while suppressing the formation of condensation polymer.